Art of recovering sulphur dioxide from gases with which it may be associated and apparatus therefor



June 15 1926.

EUSTIS Filed Feb.

IT MAY BE ASSOCIATED AND APPARATUS THEREFOR ART OF RECOVERING SULPHUR DIOXIDE FROM GASES WITH WHICH iwave;

Patented June 15,1926, 1,589,133- .umrao STATES PATENT OFFICE.

AUGIIS'IUS H. E'USTIS, OF MILTON, MASSACHUSETTS.

law or nncovnnme suurn un nroxrnn anon ensue wrrn wnrcn "n: my an ASSOCIATED AND ArrERArus 'rnnnnro'n.

- Application filed February 7, 1920, Serial No.'356,814.

' This invention relates to the art of rethe sulphur dioxide gas in-the atmosphere covering-'- sulphur dioxide from smelter contacting with the solution.

smoke or other gases with which 'it may be While I prefer to use aluminum sulphite associated, and to apparatus therefor. as the reagent for taking sulphur dioxide 1 5 Stated in general terms processes of the into solution, other salts may be used,

' character to which the present invention reand it should be understood that the invenlates, as exemplified by Letters Patent of tion in'its broader aspects is not limited to the United States No. 1,260,492, dated any particular salt but contemplates liquors -March 26, 1918; No. 1,260,493, dated March containing any soluble metallic sulphites 10 26, 1918; No. 1,265,892,-dated May 14, 1918 other than sulphites of the alkaline earths and anapplication for Letters Patent of the which reacts with sulphur dioxide to take United States filed by me April 14, 1919, the latter into the liquor, and which again Serial Number 289,857, comprise absorb- 'readily liberates sulphur dioxide under the ing sulphur dioxide gas from-smelter smoke conditions prevailing in practice. Such or other gas into water, andthen extracting conditions may, .for example correspond to 'm the sulphur dioxide from the water, and the boiling point of water or of the liquor liquefying the sulphur dioxide gas if dein which the sulphur dioxide has been dissire'd'.. These processes sis-heretofore pracsolved, with or without reduction in the tisedhave required alarge amount of water. superimposed pressure thereon.

with a correspondingly large plant and Other important conditions, hereinafter 5 large amount of heat'and power. more fully ex lained",'are that thesalt or 'The ultimate objects of thisin vention are othermaterialf should be one which will to rovide a new and more economical form with the sulphur dioxide a relatively met odof getting the'sulphur dioxide gas unstable sulphite or bisulphite which will into the solution, and of extracting the sulreadily liberate the sulphur dioxide gas at 9 phur dioxide from the solution, together moderate temperatures; and one whose sulwith apparatus therefor; and to "reduce the phate soluble, in order that insoluble precost of operation by reducing the size ofthe "cipitates may not be formed which are apt plant necessary for carrying on the process to clog-the pipes and pumps. In most cases and by reducing the volume of liquid treated -the liquor will be somewhat heated in the and consequently the amount of heat and extractor and againcooled before entering power required. the towers, and with heating and cooling it I have discovered that it'is possible'to use is diflicult to avoid oxidation and the conchemical reaction both as a means of collectsequent forming of precipitated sulphates. 35 ing the sulphur dioxide into solution, and material should therefore bev selected as a cans of liberating the sulphur di- W 'ose sulphate is soluble. .Iron sulphite,- oxide rom the solution. By using a solufor example, might be used and has the adtion of a salt, such as aluminum sulphite, vantage ofcheapness although it does not I have found that a much larger amount of take up the sulphur dioxide quite. as readily sulphur dioxide may be taken into the soluas. aluminum sulphite. It gives up the sultion than has been possible with the methods phur dioxide from the liquor practically as heretofore used. This I attribute to the easily. Sodiumsalts take up the sulphur chemical combination between thesalt and dioxide more vigorously but will not give it the sulphur dioxide which results in the 001- up as readily. ,Calcium sulphite forms in- .lection into the "solution of a mu larger soluble sulphates,and does not take up sulquantity of the sulphur dioxide gas from phur dioxide quite as well as aluminum sulmixtures of gases, such as a smelter smoke, phit'e. Copper sulphite absorbs about like or other mixtures containing sulphur diiron sulphite and gives up somewhat more oxide gas, than results from the" mere physi readily, but is expensive. Chromium and cal absorption of sulphur dioxide gas into strontium sulphites make liquors which are a liquor. I have also found that the sultroublesome and diflicult to handle. Allv phur dioxide gas can then be extracted from thingsconsidered I have found aluminum the liquor by' breaking down or decomposing sulphite the preferable materlal, with. er- I the chemical; combination, and that this can haps iron su-lphite as second choice. ut

be done by reducing the partial pressure'of it will be understood that the invention in for this aspect is not limited to aluminum sulphite andiron sulphite, but contemplates in general the soluble metallic sulphites other than sulphites of the alkaline earths. To recapitulate, therefore, it will be clear that a chemical reagent (such as metal or a metallic compound) will be suitable for application to the present invention, which is characterized by a capacity concurrently to go into solution, preferably with water, and to absorb sulphur dioxide therein, with the formation ofan unstable compound which, upon rise oftemperature (as to the boiling temperature of wateror of the solution itself) will decompose and evolve a substantial proportion of its sulphur dioxide contents, wthout appreciable susceptibility to the formation of non-decomposable or insoluble: compounds, such as sulphates.

In the accompanying drawings which illustrate apparatus for carrying out the v delivered, with the aid of a pump,

process,

Figure 1 is a diagrammatic view of the apparatus as a whole; 1

Figure 2 is a plan view .of one of the shelves in the extractor; and 1 Figure 3 is a plan View of another of said shelves.

Gases from the furnace, smelter, or other source are led through flue 1 into the hot tower 2, the principal function of which is to cool and clean the gases. From tower 2 the gases pass through pipe or flue 3 into the bottoms of towers 4, 4., 4, in parallel,

thence from the tops of these towersby pipe or flue 5 into the bottoms of towers 6 6", 6. in parallel; thence from the tops 'of these towers by pipe or flue 7 into the bottom of tower 8; and. thence by pipeor flue 9 to the stack or the atmosphere.

. The hot tower 2, the towers 4*, etc, (which may be termed the 4-group), the towers 6*, etc. (which may be termed the 6-group) and the tower 8 may all be substantially similar and may be packed with masses of broken solid' material, or otherwise so constructed that water or liquor descending through the towers will be broken up to present extensive superficial areas for contact with the gases rising through the towers. The packing material in tower 8 will preferably "be a mineral containing soluble aluminum salts, while the packing in the other towers may be an insoluble material such as coke or slag.

' \Vater or the liquor is delivered through pipe 10, aided by pump 11, into the top of tower 8 in which it trickles down over the packing in contact with the rising gas. From the bottom of tower 8 the liquor is by pipe 12 in parallel to headers or distributors at the tops of the several towers of the 6- group, and trickles down through said towers over the packing. From the bottoms of the towers of the 6-group the liquor flows by pipe 13 to the tops of the towersof the 4-group through which it passes in parallel, as before, thence flows by pipe 14 into a storage tank 14, and thence aided by pump 15 if necessary, to the top of tank 16.

Inasmuch as the liquor-passing through the towers first enters tower 8, where it flows over the mineral containing soluble aluminum compounds, it will take alumina into solution probably as a sulphite, and the liquor passing through the outer towers will therefore also be an aluminum sulphite solution. The material which I prefer to use in tower 8 to produce the aluminum sulphite solution is bauxite, but other mateif desired, by connecting pipe 14 to the hot tower 2 in, similar fashion.

The tank 16 is a combined douche tank and extractor, the upper part constituting a'douche tank to cool the gases rising from the bottom of the tank, and the lower part constituting an extractor chamber for extracting the SO, gas from the solution. This preferred arrangement provides a cooling chamber mounted directly on top of the extractor chamber to receive gas directly therefrom; but the douche tank cooling chamber and the extractor chamber might be. made in separate tanks connected by a pipe or flue.

The tank 16 is provided with a series of shelves or pans 17 having a central opening 18 for the passage of the rising gases, and shelves or pans 19 of less diameter than the tank 16 to leave an annular opening around the periphery .for the passage of gas. The shelves 17 and 19 are alternately arranged as shown, and each shelf overlaps the opening of the next shelf, thus roviding a tortuous or sinuous passage or the gases rising through the tank. The shelves are also perforated with a large number of small holesthrough which the solutions.

flow, broken up into small streams or dropslike rain, to expose superficially extensive surfacesf Other arrangements ,of shelves which will produce a tortuous path for the ue .for the extracted SO gas lea ing cham- Thus the liquor flows in a-continuous cir- 7 cuit or cycle and may be used over'and over again without substantial loss of the aluminum sulphite in solution.

If its found necessary or advantageous to carry on the extraction in tank 16 at pressures below atmosphere, the pipe 20 may be connected toa vacuum pump and if the extracted gases are to be liquefied they. may be delivered from pipe 20 to suit-' able compressing and condensing apparatus.

The furnace or other gases containing sulphur dioxide first enter the towers of" the 4-group and come in contact with the descending solution of aluminum sulphite which reduces the temperature. of the gases and absorbs a certain amount of sulphur dioxide gas which enters into chemical combination with the sulphite solution. The gases then pass through the towers of the G-group and give up more of their sulphur dioxide gas, and finally through tower 8 in which substantially all the remaining sul- .phur dioxide as is taken out. The gases will also have ee'n somewhat cooled at each stage. r I

I have found that aluminum sulphite is admirably adapted to the purpose of ab sorbing sulphur dioxide, as it has a marked capacity, in solution in water, of combining with and taking up sulphur dioxide gas, and the aluminum sulphate, if formed by oxidation, is soluble. I-believe also that the presence of the bis ulphite formed by the combination of aluminum sulphite with the sulphurxdioxide increases the ca acity of the solution to take up sulphur] ioxide. The bisulphite solution formed with aluminum sulphite is also comparatively unstable, and

when subjected in the'extractor .to the effect of reduced partial ressure of sulphur dioxide by dilution 0 the gas, supplemented by heat if necessary, as hereinafter described, sulphur dioxide gas readily-comes out of the solution.

Although I have mentioned putting a mineral, such as bauxite, containing soluble aluminum compounds into tower 8 to pro duce an aluminum sulphite solution, baux ite dissolves soslowly that I recommend supplementing it by putting freshly precipitated aluminum hydrate, or equivalent compounds, into the cooling pond 24 to form a solution of s'ulphites which will thence be circulatedthrough the towers as described. Or, if desired, the solution of sulphites could be made up elsewhere and circulated through the towers. It will also tial pressure of t e sulphur dioxide in the gases or atmosphere contacting with the liquor. The gas-used "for the dilution should preferably be one that will condense more easily than the sul hur dioxide and therefore be removed be ore the sulphurdioxide is compressed; otherwise the volume of the diluting gas would. have to be carried through the compressors which would necessitate greatly enlarged compressing ap-. paratus, and a greater amount of power than if only the sulphur dioxide gas were compressed.

Steam is a gas which is convenient to use and admirably fulfills the requirements for diluting the atmo here in contact with the liquor. According y I direct a copious flow of exhaust steam from a large engine or" quantity that will condense and should prefe'rably be in excess of what will condense in the tank 16, in order to insure the maximum dilution of the atmosphere intank l6 and to obtain a substantially complete liberation of sulphur dioxide "from .the liquid. The exhaust steam will also furnish heat which aids the extraction, and the greater part of the steam will be condensed in the 1 upper part of the extractor where it. comes in contact with the relatively cool incoming liquor. Thus the tank 16 performs the duty 'of an ordinary condenser, and the combination ofthe steam engine with the extractor tank is therefore advantageous and economical both from the int of view of furnish-- ing an excellent dlluent for the extraction.

of the. gas, and of the steam of the engine.

If desired the extraction may be carried condensing of the on under pressures below atmospheric and to this end a vacuum pump 25 may be connected topipe 20. The vacuum contributes.

to the extraction of the sulphur dioxide gas. Vacuum, however, is not necessary with the present process, as the dilution of the atmosphere in contact with the liquor and the resulting reduction of the partial pressure of the sulphur dioxide in the gases over the liquor, will Work satisfactorily when the extraction is carried on at, or

even above, atmospheric pressure. In this case, the pump 25 would of course be dispensed with or a relief pressure valve provided in its place.

The extraction of the gas may be accomplished by the dilution, with or without heat and vacuum or either of them.

By making the extractor very large, and prolonging the time the liquor is exposed to treatment therein, a very large percentage of the total sulphur dioxide in the liquor may be extracted at'each cycle, and it will be a commercial question to determine for each plant what will be .the most economical size of extractor and therefore the proportion of sulphur dioxide that will be removed each time the liquor is circulated. The first part of the sulphur dioxide to be extracted comes off easier than the last part. On the other hand, the greater the amount of sulphur dioxide which is removed during each cycle, the less will be the volume of liquor that'must be handled, and the lessthe liquor the less power and heat, required. If the extraction is prolonged too far, a precipitate maybe formed that will be hard to re dissolve, and this should be avoided.

Although'the reactions which take place in the process are obscure, and cannot be stated with entire certainty, I believe that the aluminum sulphite in the solution forms a chemical combination with the sulphur dioxide and becomes bisulphite in the presence of an excess of sulphur dioxide gas, and so takes up sulphur dioxide gas out of the smelter smoke or the like; and that when the atmosphere in contact with the solution is diluted, thus reducing the partial pressure of sulphur dioxide gas in the atmosphere contacting with the solution in the jextractor, the bisulphite breaks up, becoming a ,normal sulphite, and in so doing liberates the sulphur dioxide, aided if desired by heat, or vacuum, or both. y

To accomplish the desired result, the chemical used, whether aluminum sulphite or some other material, should be adapted to form a relatively unstable bisulphite and one which will react within a relatively small range of temperatures; that is, one

which will combine with the sulphur di- I oxide gas and absorb itat moderate tempercontacting with the solution in the extractor atures as the gas comes in contact with the coolerliquor in the towers, and which will also decompose at moderate temperatures in the extractor, preferably not above the boiling point of the liquor. The material should also be one which will remain soluble and will not precipitate at "the temperatures used.

And the gas used to dilute the atmosphere shouldbe supplied in copious quantities and should 'preferablybe one which, like steam, will condense more quicklythan sulphur (11- oxide gas, so that it may be condensed out and wholly separated from the sulphur dioxide gas before the latter passes to thecompressor. By using H the exhaust steam from an engine a substantial economy is effected by getting valuable work out of the exhaust steam in using it as a diluent and source of heat in the extractor, incidental to the condensing of the steam. I

I claim: v

1. The art of obtainingsulphur dioxide from smelter smoke or other gases with which it may be associated, which comprises absorbing the sulphur dioxide in a liquid, in the presence of a' metallic compound adapted to form therewith an unstable sulphite, soluble in said liquid and not susceptible to oxidation to an insoluble sulphate, and thereafter liberating sulphur dioxide from said sulphite by decomposing the resulting solution. i I

2. The art of obtaining sulphur dioxide from smelter smoke or other gases with which it may be associated, whichcomprises absorbing the sulphur dioxide in water in the presence of a metallic com pound, adapted to form therewith an unstable sulphite, soluble in water at'moderate temperatures and not susceptible to oxidation to an insoluble sulphate, and again to decompose at temperatures not exceeding the boilin point of water at t-liepressure employed; and thereafter liberating sulphur dioxide therefrom the compound.

3. The art of obtairiing sulphur dioxide b decom osin y P a:

from smelter smoke .or other gases with metal, and thereafter liberating sulphur dioxide by decomposing the compound.

4. The art of obtaining sulphur dioxide from smelter smoke or other gases with which it may be associated, which comprises absorbing the sulphur dioxide in a liquid solution containin aluminum sulphite, and thereafter liberating sulphur dioxide by decomposing the compound formed, with the 5 aluminum sulphite.

5. The art of obtaining sulphur dioxide from smelter smoke or other gases with which it may be associated, which comprises absorbing the sulphur dioxide gas in a liquid, and thereafter reducing the pantial pressure of sulphur dioxide gas in the atmosphere contacting with the liquid by diluting said atmosphere with a gas other than sulphur dioxide in such volume as to effect, a substantially complete liberation of the sulphur dioxide from, the liquid.

6. The art of obtaining sulphur dioxide .from smelter smoke or other gases with which it may be associated, which comprises absorbing. the sulphur dioxide gas in a liquid and thereafter reducing the partial pressure of sulphur dioxide gas in the at-f mosphere contactin with'the liquid by d luting said atmosp ere with a condensible gas other'than sulphur dioxide inaquantity in excess of that which will be con densed, thereby. liberating sulphur dioxide diluting said atmosphere with steam in a quantity in excess of that.wh-ieh will be condensed, thereby liberating sulphur dioxide from the liquid, and thereafter condensing out the steam leaving .sulphur dioxide gas.

. thereafter reducing the partial pressure of- 8. The art of obtaining sulphur dioxide from smelter smoke or other gas with which it may be associated, which comprises absorbing the sulphur dioxide gas in a liquid,

sulphur dioxide gas in the atmosphere contacting with the liquid by diluting said atmos here with a condensible gas other than sulp ur dioxide in 'a quantity in excess of that which will becondensed, said gas'being condensible at lower pressure. and higher temperature than sulphur dioxide gas, thereby liberating sulphur dioxide,from the liquid, and thereafter condensing out the diluting gas leaving sulphur dioxide gas.

9. The .art of obtaining sulphur dioxide from smelter smoke or other gases with which it ma be associated, which comprises absorbing the sulphur dioxide in a liquid solution containing soluble metallic s phites' other than sulphites of the alkaline earths, and thereafter reducing the partial pressure of sulphur dioxide gas in the atmosphere contacting with the liquid by diluting said atmosphere with a gas other than sulphur dioxide in such volume as to effect a substantially complete liberation of the sulphur dioxide from the liquid.

10. ,The art of obtaining sulphur dioxide from smelter smoke or other gases with which it may be associated, which comprises.

absorbing the sulphur dioxide in a liquid solution containing soluble metallic sulphites othervthan sulphites of the alkaline I earths, and thereafter reducing the partial pressure of sulphur dioxide gas in the atmosphere contacting with the liquid by diluting said atmosphere with steam in a quantity in excess of that which will be condensed, thereby liberating sulphur dioxide from the liquid, and thereafter condensing out the steam leaving sulphur dioxide... v

11. The art. of obtaining sulphur dioxide from smelter smoke or other gases with .lwhich it maybe associated, which coniprises absorbing the sulphur dioxide in a liquid solution containing aluminum sulphite to form with the sulphur dioxide an aluminum bisulphite, reducing the partial pressure of the sulphur dioxide gas in the atmosphere contacting with the. bisulphite solution by diluting said atmosphere with a copious su 'ply of steam to decompose the aluminum bisulphite and liberate sulphur dioxide, and condensing out the steam leaving sulphur dioxide.

12. Apparatus for obtaining sulphur dioxide from a solution containing the same, comprising a combined extractor chamber and exhaust steam condenser, means for delivering the solution into the extractor chamber, and means adapted to deliver ex haust steam to said chamber in an amount exceeding that of the solution under treatment, means for withdrawing residual vapors, from the extractor, and means for withdrawin liquids therefrom, thereby conducting sai liquids and vapors in-countercurrent relationship, whereby the combined heat of the exhaust steam and the reduction of the partial pressure of sulphur dioxide in the atmosphere within the extractor resulting from its dilution by steam will liberate sulphur dioxide gas from the solution, and the solution will in turn condense the exhaust steam. v13. Apparatus .for the concurrent condensation of exhaust steam and recovery of sulphur-dioxide from solutions containing the same, comprising an extractor chamber, means for circulating said solution through the extraction chamber, means for drawing exhaust steam into and through the extraction chamber, under reduced pressure, means for facilitating the free passage of said steam in intimate contact with said solution, and means for withdrawing the evolved and uncondensed vapors from said extractor chamber. y

14. Apparatus for the concurrent condensation of exhaust steam and recoveringthe sulphur dioxide from a solution containing the same, comprising an extractor chamber, means for delivering the sulphur the concurrent condensame comprising an extractor chamber, means for delivering the sulphur dioxide solution to the extractor, a steam turbine exhaust, means connecting the exhaust to said. extractor chamber to provide for the free passage of steam therethrough and in intimate" unobstructed contact with said sulphur dioxidew solution, suction means for withdrawing uncondensed va ors from said extractor and adapted therebnto create and maintain a partial vacuum, substantially -undiminished throughout said extractor and exhaust, and means for withdrawing the extracted solution and condensate .from said extractor.

16. Apparatus for the concurrent condensation of exhaust steam and recovery of sulphur dioxide from a solution containing the same, comprising an extractor'chamber, in let means for introducing the sulphur dioxide solution in widely distributed condition into the upper portion of the extractor, a steam turbine exhaust, means connecting the exhaust'to the extractor chamber toprovide for the free passage of steam from said exhaust into the lower portion of the extractor chamber and in intimate contact With said sulphur dioxide solution therein, suction means for withdrawing the uncondensed vapors .from the upper portion of said extractor, and adapted to maintain .a

'partial vacuum substantially undiminished throughout said extractor and turbine exhaust, and means for withdrawing the extracted solution and condensate from the lower portion of said extractor chamber.

Signed by-me at Boston, Massachusetts, this 2 day of February, 1920.

AUGUSTUS H. EUSTIS. 

